Catalase has been one of the most intensely studied enzymes. This heme-containing redox protein is found in nearly all animal cells, plant cells and aerobic microorganisms. This enzyme is probably best known for its catalatic activity, breaking down potentially damaging hydrogen peroxide into oxygen and water. By preventing excessive build-up of hydrogen peroxide in cells, catalase permits the required cellular processes that produce hydrogen peroxide to take place. Catalase also possesses peroxidase activity, also known as peroxidatic activity, which allows catalase to oxidize certain low molecular weight alcohols in the presence of small amounts of the cofactor hydrogen peroxide.
A kit for assaying catalase activity via the substrate AMPLEX-RED™ is commercially available (Molecular Probes, Inc. 4849 Pitchford Avenue, Eugene, Oreg.). In this assay, catalase first reacts with hydrogen peroxide to produce water and oxygen. The AMPLEX-RED™ reagent is then added to react with any unreacted hydrogen peroxide in the presence of horse radish peroxidase to produce the highly fluorescent product resorufin (Zhou et al. Anal. Biochem. 1997 253(2):162–8). Thus, in this assay, as catalase activity increases, the signal from the resorufin decreases.
Modifications to catalase via acetylation or guanidation result in a loss in catalatic and peroxidatic activities. The catalatic activity of catalase has also been shown to be photoinactivated in vitro (Mitchell, R. L. and Anderson, I. C. Science 1965 150:74); Chen et al. Photochem. Photobiol. 1981 34:125–129; Feierabend, J. and Engel, S. Arch. Biochem. Biophys. 1986:251:567–576) and in cultured cells (Zigman et al. Photochem. Photobiol. 1996 63:818–824 and Giordani et al. Redox Report 1997 3:49–55) upon irradiation with high doses of ultraviolet or visible light.
It has now been found that mammalian catalase oxidizes a broad range of substrates in the absence of hydrogen peroxide. Further, it has now been found that exposure of mammalian catalase and substrates to low doses of ultraviolet light accelerates oxidation of the substrates.